Microwave phase shifter having ridge waveguide with moveable wall



Feb. 15, 1966 J, w s 3,235,821

MICROWAVE PHASE SHIFTER HAVING RIDGE WAVEGUIDE WITH MOVEABLE WALL Filed Oct. 9, 1961 4 Sheets-Sheet 1 BL T 6.0- h b z'- FIG. 1

ba =0.2" V

II A o =|.s75 A I40 (I) f b o.2" o 2 Z I I00 l J m \3.5KMC O Z E 80 RECTANGULAR 4.oKMc m GUIDE l3.5KMC 4o 4.0KMC

RIDGE GUIDE G'OKMC INVENTOR. H A WALL DISPLACEMENT IN mc EBSY ERNEST WILKINSON FIG. 2 {m ATTORNEY Feb. 15, 1966 E. J. WILKINSON 3,235,821

MICROWAVE PHASE SHIFTER HAVING RIDGE WAVEGUIDE WITH MQVEABLE WALL 4 Sheets-Sheet 2 Filed Oct 9, 1961 PHASE l U 0.2" L

f 3.5 KMC IMPEDANCE A-WALL DISPLACEMENT IN INCHES wmmmwma Z- mmaim O O 0 m 8 6 o m m E 0 W Y W z 08 E W P 2 3 M m N P T 0 9 WK l N NW T n "2 m A T: 1 J M Nslllll II II u "m 5 E 8 H H w o m/ 00 M E '0 ll 0 I Y a B 9 5 l H I C z 8 2| l 0.. N a G N n 7 C l m x F H s N A 6 R T T wM||||||||||| TD UN CE Feb. 15, 1966 E. J. WILKINSON 3,235,821

MICROWAVE PHASE SHIFTER HAVING RIDGE WAVEGUIDE WITH MOVEABLE WALL Filed Oct. 9. 1961 4 Sheets-Sheet 3 FIG.5

\IVIIIL 26 FIG. 6

INVENTOR.

ERNEST J. WILKINSON A TTORNE Y E. J. WILKINSON I 3,235,821 MICROWAVE PHASE SHIFTER HAVING RIDGE WAVEGUIDE WITH MOVEABLE WALL 4 Sheets-Sheet 4 Feb. 15, 1966 Filed Oct. 9, 1961 FIG. /0 CULATED FOR 4" LONG PHASE SHIFTING SECTION ONLY CALCULATED FOR EACH 0F fTWO 2" LONG TRANSITION SECTIONS L M S E XL TH AP L UL 5 AO CT DA E H R LT AF ATI. EOH MT I O O 0 O 0 0 Q 0 O O 0 Q 6 5 4 3 2 l INVENTOR.

ERNEST J. WILKINSON A-WALL DISPLACEMENT IN INCHES A TTORNEY FIG. 9

United States Patent 3,235,821 MICRGWAVE PHASE SHIFTER HAVING RIDGE WAVEGUIDE WITH MOVEABLE WALL Ernest J. Wilkinson, Westwood, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Oct. 9, 1961, Ser. No. 143,847 17 Claims. (Cl. 33331) This invention relates generally to phase-shifting apparatus and is more particularly concerned with phase shifters operable at microwave frequencies and capable of handling high power signals.

There are many applications for phase shifters in microwave communication systems, a representative example being in phased-array radar systems where they are employed to change the phase of signals in a plurality of channels preparatory to combination to form the main beam signal. This phase shift of signals from a multiplicity of antenna elements makes it possible to steer the radar beam, while maintaining the antenna structure stationary. In order to steer the beam, it is necessary that the phase shift in the several channels be changed simultaneously, and since radar systems of this type are normally higher power systems, in the megawatt range, the phase shifter must be capable of handling high power signals.

Heretofore, ferrite phase shifters have been used in this application because they are capable of handling relatively high power, and the phase shift can be varied electronically, a feature essential to attaining a suitable scanning rate. Phase shifters of this type, however, have a number of undesirable characteristics which limit their usefulness. They are characteristically heavy and bulky, and require a considerable amount of driving power to perform the phase shifting function at a rapid rate. The ferrite material absorbs a portion of the signal causing heating toward a temperature approaching the Curie temperature of the ferrite, which, in turn, affects its phase shifting properties. To overcome this difiiculty, it is necessary to cool the ferrite elements, which contributes further to the size and weight of the phase shifter, and the required driving power. When it is remembered that a phased array radar system requires a phase shifter in each of a large multiplicity of channels, it can be seen that the ferrite phase shifter leaves much to be desired.

With an appreciation of the shortcomings of available phase shifters, applicant has as a primary object of this invention to provide an improved phase shifter capable of varying at a relatively high rate the phase of a microwave si nal.

Another object of the invention is to provide a phase shifter with high power handling capabilities whose characteristics remain essentially constant during operation.

Another object of the invention is to provide a phase shifter having the foregoing characteristics whose phase shift can be controlled electronically with relatively little control power.

Still another object of the invention is to provide a phase shifter that is more compact, lighter in weight, and less expensive than known high power phase shifters.

Briefly, the phase shifter in accordance with the present invention utilizes the well known property of a waveguide that the phase shift per unit length of a guide operating in the TE or TM mode can be controlled by varying the cut-off wavelength of the guide. As is well known, the cut-off wavelength is a function of the physical dimensions of the guide, and consequently the cut-off wavelength and attendant phase shift may be changed by changing the cross-sectional geometry of the waveguide, such as by varying the width of the guide. In the present invention, phase shift is produced by changing the spacing between the sidewalls of the guide by physically expanding or contracting the. sidewalls from their normal position.

However, such a variation in the wide dimension of a rectangular guide is inherently accompanied by a change in impedance which cannot be tolerated because of the reflections which would occur at the input and output ends of the waveguide section. To overcome this difficulty, a section of ridge waveguide, having a ratio of ridge-towaveguide width approaching one (ridge very close to sidewalls) is used, applicant having found that with this configuration, the impedance is very nearly constant over a large range of phase shift. Moreover, with the ridge very close to the sidewalls, a very small displacement of the sidewalls produces a significant change in phase shift. These properties permit using thin, flexible sidewalls in the waveguide section, and the use of electronically controllable transducers to produce the small displacement required to vary the phase by the desired amount at relatively high rates. The transducer may take the form of an electromagnetic audio speaker, with the diaphragm 'secured to the flexible sidewall, whereby the degree of phase shift is controlled in response to the signal applied to the speaker. Alternatively, an electrostatic transducer, including a pair of plates positioned closely parallel to the flexible sidewalls, may be employed to move the sidewalls in response to a signal applied to the plates. In each case, the low inertia of the sidewalls allows them to be driven at relaively rapid rates to obtain a correspondingly rapid phase change in the microwave signal transmitted through the device. Because the power handling capability of the phase shifter is dependent on the spacing between the ridges of the guide, and is not materially affected by the narrow spacing between the ridge and, the sidewalls, the device may be operated at high signal power levels.

Other objects, features and advantages of the invention, and a. better understanding of its construction and operation will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a family of curves for ridge waveguide in which the cut-off wavelength normalized to the waveguide width is plotted against the ratio of ridge-to-waveguide width;

FIGURE 2 is a family of curves showing the characteristic impedance as a function of wall displacement for ridge waveguide and waveguide of rectangular crosssection at different frequencies;

FIGURE 3 is a plot showing the phase shift per unit length and the characteristic impedance, both as a function of wall displacement, for a ridge waveguide;

FIGURE 4 is an elevation front view of a phase shifter constructed in accordance with the invention, with the transducers removed for clarity;

FIGURE 5 is a plan cross-sectional view taken along line 5-5 of FIGURE 4;

FIGURE 6 is a cross-sectional view taken along line 66 of FIGURE 4;

FIGURE 7 is a perspective view, partially cut away, of one end of the phase shifter of FIGURE 4;

FIGURE 8 is a plot of guide wavelength as a function of cut-off wavelength for different configurations of ridge waveguide;

FIGURE 9 is a plot of phase shift as a function of wall displacement for a device constructed in accordance with FIGURE 4; and

FIGURE 10 is a cross-sectional view illustrating an electrostatic transducer for obtaining wall displacement.

Before describing a specific device for accomplishing the foregoing objects, it will be helpful to an understanding of the invention to review the general principles underlying its operation. It is well known that the phase shift experienced by a signal passing through a waveguide of length l is simply I O 360 X where is the wavelength within the guide. The guide wavelength differs from the free space wavelength A of the signal, but is related to it by the following expression:

A. r \E A not produce a corresponding change in the characteristic impedance Z, of the waveguide, for such a change would cause reflections to occur at the input and output ends of the guide. The characteristic impedance of a rectangular guide operating in the TE modes varies in accordance with the following expression where the constant K is a function of the waveguide crosssectional geometry. It is therefore necessary to use a waveguide having properties such that changes in crosssection for the purpose of changing the value of A produce compensating changes in K such that Z remains approximately constant and only the phase is varied. In rectangular waveguides, changing the width of the guide to obtain a shift in phase unfortunately causes K and A /A to vary in the same direction, producing a large change in Z This tendency for K and A to vary in thesame direction is characteristic of virtually all of the conventional waveguide cross-sections normally used as transmission lines. Applicant has discovered, however, that for ridge waveguide, having a ratio of ridgeto-waveguide width which approaches one (i.e., ridge very close to the sidewalls), capacitive coupling from the ridge to the wall causes K to vary in the direction opposite to A /A causing Z to remain very nearly constant. It has been found, also, that this form of waveguide is considerably more sensitive than conventional rectangular waveguides in its ability to produce a given change in 'A /A per unit of wall displacement.

That the phase sensitivity of a ridge waveguide is greater than that of a rectangular guide is borne out by the family of curves of FIGURE 1 in which the cut-off wavelength A normalized to the waveguide Width a has been plotted against the ratio of ridge-to-waveguide width a /a In conventional transmission lines, ratios of a a in a range of 0.3 to 0.4 are normally used. These curves show that if ratios of a /a approaching unity are used, small changes in the ratio produce large changes in X This property would be undesirable for transmission line applications, but is ideal for a phase shifter in which it is intended to obtain phase shift by varying the dimension al as by vibrating the side walls of the wave guide. The curves of FIGURE 1 also show that the greater the ratio of ridge spacing to waveguide height, b /b the greater the change in k, for a given change in a The slope of the cut-off wavelength versus a curve, which is a measure of sensitivity, is shown to be considerably different for different b /b ratios. When the condition which obtains in a conventional rectangular guide, the curves show that 7t =2a; i.e., the cut-off wavelength is twice the width of the rectangular guide as mentioned earlier. The slope of this curve, Ax /A01 is equal to 2. If the ratio b /b is increased by a factor of 10, it will be noted that the sensitivity is also increased by a factor of 10.

While the curves of FIGURE 1 indicate that a ridge Waveguide will produce significant phase change with a small sidewall displacement, to be useful as a phase shifter it is essential that this increase in sensitivity not be accompanied by a corresponding increase in impedance variation with wall displacement. When the ratio a /a is approximately equal to one, and the value of il -0 c is much less than one, the characteristic impedance Z, for a double ridge guide, defined on a voltage-current basis, may be written:

77112 A 2 (t) (t) Eq. 2 In Equation 2, C is the discontinuity capacitance at the edges of the ridge and P is a multiplying factor which accounts for the proximity effect of the waveguide wall to the ridge. Values for C and P have been published by Iamieson and Whinnery in an article entitled Equivalent Circuits for Discontinuities in Transmission Lines, appearing in Proceedings of IRE for February 1944.

Equation 2 is plotted in FIGURE 2, for three different frequencies, as a function of sidewall displacement,

for a double ridge guide having a spacing between ridges of 0.2 inch and a ridge width, a of 1.875 inches. It will be seen that for zero wall displacement the ridge guide degenerates into a rectangular guide having dimensions .2 1.875 inches. For this situation, A =2a and the first term in the denominator of Equation 2 is equal to zero. As a consequence, the impedance changes significantly with changes in width of this rectangular guide as shown by the dotted curves of FIG. 2.

As the walls are displaced outwardly from the ridge by a small amount, a'sharp discontinuity in impedance occurs, for A is no langer equal to 2a and the cos 60 h term is large because of the discontinuity capacitance C and the proximity factor P. The larger the ratio of ridge spacing to the height of the movable wall, the more significant this term becomes since C increases with this ratio. The foregoing accounts for the steep portion of the impedance curves for the ridge guide. As the wall is displaced further from the ridge, two effects come into play. The proximity factor P decreases and the cut-off wavelength k increases. These effects produce offsetting changes in the denominator of Equation 2 tending to keep Z constant. For a rectangular guide, where the cosine term is always zero, Z decreases steadly with increasing M. It will be noted from a comparison of the impedance curves for the ridge guide with those of the dotted curves; for the rectangular guide that the impedance of the ridge guide is also less sensitive to changes in frequency than a rectangular guide of comparable dimensions. This is partially due to the fact that over the indicated range of Wall displacements where Z, is substantially constant, h is somewhat higher for the ridge cross-section, and, hence, changes in A are less effective in changing the value of the frequency dependent x /A factor in Equation 2.

The discontinuity in the impedance limits the smallest wall displacement that can be used. The largest wall displacement is limited by the fact that the phase sensitivity falls off, approaching that for rectangular guide, as the wall is moved away from the ridge. The curves of FIGURE 3, showing differential phase shift per inch of waveguide and characteristic impedance plotted against wall displacement, indicate that a minimum displacement of 0.010 inch and a maximum displacement of 0.030 inch, for example, would yield a 37 to 41 ohm variation in impedance and approximately 14 per inch dilferential phase shift at a frequency of 3.5 kilomegacycles.

Small displacements of this order of magnitude are readily obtainable by forming the sidewalls of the phase shifting waveguide section of thin, sheet metal, the displacement of which can readily be controlled by audio transducers, such as an electromagnetic speaker, at frequencies of several hundred cycles per second. A practical embodiment of the foregoing principles in a phase shifter of the moving wall type is shown in FIGURES 4, 5, 6, and 7. The device consists of a section of double ridge waveguide 10, the lower and upper ridges 1'2 and 14 of which are just slightly narrower than the width dimension of the guide. By way of example, in a phase shifter havin an overall length of 8 inches, and a guide width of 2 inches, the width of the ridge in the wider center section is 1% inches. Throughout the central section of the device, the sidewalls 16 and 18 are formed of thin conductive material so as to have a low mass and be readily movable in and out with respect to the ridges 12 and 14 in response to a small force. The walls 16 and 18, each consisting of a fiat rectangular sheet, are joined along their upper and lower edges to the top and bottom walls of the waveguide with very thin conductive hinges 20, 22 and 24, 26, formed, for example, of aluminum foil. These hinges, which extend the full length of the phase shifting section, may be secured to the movable wall by sandwichi-ng the foil between a thin aluminum strip 28 and the movable wall and securing the strip and wall together by means of rivets 30. Although these hinges are relatively fragile, being made of thin foil so as not to appreciably limit the motion of the movable walls in and out with respect to the ridges of the guide, they have proven to be very durable in this application.

From an electrical point of view, it is not necessary to hinge the ends of the movable sidewalls to the waveguide, since the wall currents run parallel to the gap. However, for mechanical reasons, primarily to prevent flutter of the end portions of the movable sidewalls when driven at a point near the center, it may be desirable to also hinge the ends of the movable wall to the fixed portion of the device. Aluminum foil hinges 32 and 34 may be used for this purpose, or, since it is not essential to have a conductive connection between the ends of the movable walls and the fixed portion of the guide, the ends of the plate may be secured by an insulating flexible tape. With the movable walls thus mounted on the ridged port-ion of the guide structure, the entire wall is allowed to move in and out parallel to itself in piston-like fashion. By employing hinges, it is easily possible to achieve a range of travel approximately one-quarter inch for each of the walls, more than adequate to obtain the 14 per inch differential phase shift alluded to earlier in the consideration of FIGURE 3.

Conventional fixed recta-ngular-to-square ridge guide transitions 40 and 42 are joined to the ends of the movable wall section, each of the transitions including tapered ridges 44 and 46 having a thickness at the junction of the transition to the movable wall section equal to the thickness of ridges 12 and 14 at this point. To minimize thediscontinuities at the input and output ends of the moving wall section due to the movement of the walls, which would otherwise set up reflections which would tend to add or subtract in accordance with the varying phases being introduced by these sections, ridges 12 and 14 are tapered at both ends from the width of ridges 44 and 46 to the full width of ridges 12 and 14 at the center section. This tapered portion, indicated at 12a and 14a, extends over a length of approximately 2 inches in a phase shifter having a movable wall section 8 inches long. At the input end of this tapered section the ridges 12a and 14a have a width of .562 inch, giving a ratio of a /a of approximately 0.3. At the output end of the taper, the ridge width is of the order of 1.875, giving a ratio of a a which approaches unity. It will be seen from the curves of FIG- URE 1 that for a ratio of a /a equal to about 0.3, A is much less sensitive to changes in a than when the ratio approximates unity. Furthermore, the nominal value of h is very much higher. This means that for a given operating wavelength A, changes in h will produce much smaller changes in k These effects are illustrated in FIGURE 8 where the familiar curve of guide wavelength versus cut-off wavelength [Equation 1] has been plotted for the dimensions used in the example of FIGURES 2 and 3. For a given wall displacement, which is the same at both ends of the tapered section 12a, the cut-off wavelength change at each end has been marked on the curve. It is significant to note the much smaller change in h that occurs at the input end of the transition where a /a is approximately equal to 0.45, and that there is virtually no change in the guide wavelength at this end. By virtue of this, it is possible to break a fixed wall of a guide having the crosssection of the input end and start a moving wall guide of the form shown in FIGURES 47 without introducing a serious electrical mismatch. Thus, the increase in sensitivity insofar as producing changes in k with wall displacement is concerned, can be introduced gradually by tapering the ridge width until (1 a approaches unity.

Returning now to the description of the device, with particular reference to FIGURES 5 and 6, the spacing of the thin sidewalls16 and 18 from the edges of the ridges 12 and 14 is varied by one or more electromagnetic transducers 50, such as an audio speaker having a permanent magnet 52, a signal coil 54, and a cone diaphragm 56. As shown in FIGURE 6, a transducer is provided for each of the sidewalls, the diaphragm 56 being cemented or otherwise secured to the outer surface of the walls at a location generally equi-distant from the top and bottom edges of the sidewalls. The magnets of the speakers are supported on a frame 58 which generally encircles the waveguide section, this frame, in turn, being supported on blocks 60 and 62 respectively positioned on the top and bottom walls of the waveguide section. The frame 58 and blocks 60 and 62 are so arranged that the quiescent position of diaphragm 56 (i.e., with no signal current in coils 54) positions the walls 16 and 18 from ridges 12 and 14 to give initial air gaps of approximately inch in width. By selecting a transducer with suitable properties, the diaphragm 56, upon energization of the transducer, is capable of moving at least inch to either side of the aforementioned quiescent position, whereby the gap between the sidewall and the ridgesmay be varied from a minimum width of approximately inch to a maximum of inch. This V inch range of wall displacement is sufficient to achieve phase shifts of 5 per inch of waveguide, exclusive of the transitions (see FIGURE 9). For the dimensions assumed in the example of FIGURE 3, this can be increased to about 20 per inch if the ti /b ratio is increased from its value of two in the embodiment of FIGURES 4 to 7 to a value of ten.

When the voice coils 54 are energized from a suitable modulator (not shown) the diaphragm 56 of the two speakers, and consequently the sidewalls secured thereto, are displaced from their quiescent position by an amount depending on the amplitude and polarity of the signal current. With maximum current of one polarity, for instance, the sidewalls are both moved inwardly to give a minimum spacing between the sidewalls and the ridges at which the cut-off wavelength h is at its minimum value. When the signal current is of the same magnitude but of opposite polarity, both sidewalls are moved outwardly, causing a maximum gap width between the sidewalls and the ridges and a longer cut-off wavelength. Thus, by controlling the amplitude and polarity of the signal current in the transducers, the cut-off wavelength w is varied between two limiting values. This variation in cut-off wavelength is accomplished by a variation in guide wavelength, A and as shown by Equation 1, the change in guide wavelength causes a change in phase in the signal transmitted through the device.

It will be appreciated that the phase shift per unit length is not uniform throughout the length of the phase shifter because there is not the same change in cut-01f wavelength, A for a given wall displacement in the transition sections as there is in the section in which the ridges are of uniform width. However, the total change in phase produced by the device is the sum of the phase change caused by the two transition sections and that produced by the central section. Choosing a given incremental change in a say from a =l.875 inches to 42 :2 inches, and a known linear variation in the width in the tapered section, the phase shift introduced by the transition sections and the central section can be readily calculated. The calculated phase shift for each of the two transition sections, and the calculated phase change for the central section, and their sum, are shown in the dotted curves of FIGURE 9. It will be seen that the experimentally measured phase shift, shown by the solid curve of FIGURE 9, measured at 6000 megacycles, is in good agreement with the calculated value.

Although the satisfactory results shown in the curve of FIGURE 9 were obtained with a single transducer 50 secured to each of the movable sidewalls, it may be desirable in some applications to drive the sidewalls with a bank of several smaller transducers distributed along the length of the movable wall in the manner illustrated in FIGURE 5. This may be particularly important in situations where it is desirable to vary the phase at the higher audio frequencies. Each of the smaller speakers with its higher resonant frequency and lower mechanical inertia would be capable of deflecting a small section of the wall to a greater amplitude at the higher frequency with a given available force. Thus, if the banks of transducers, one on each sidewall, are driven in parallel, it is possible to obtain a higher rate of scanning of phase shift for a given driving force. Moreover, a distributed bank of smaller speakers would tend to move the entire wall parallel to itself in a piston-like manner and eliminate the tendency of the ends of the wall to flutter.

The power handling capability of a phase shifter constructed as described hereinabove is largely determined by the electric field intensity at the center of the ridges of the ridge waveguide. For the example shown in FIG- URES 46,in which the ridge spacing is A; inch, at the minimum wall displacement the calculated power handling capability is approximately 0.4 megawatt. If the corners of the ridges are rounded to a radius of the order of 0.005 inch, maximum field gradient occurs at the center of the ridge rather than at the corners, thus precluding breakdown at the corners of the ridge.

Although electromagnet transducers have thus far been described, with either a single unit on each wall, or a bank of transducers distributed along each wall, other configurations of electromagnetic transducers may be used, or electrostatic transducers may be employed, without departing from the general principles and spirit of the invention. For example, instead of the movable wall section being straight as shown in FIGURES 4-6, it may be bent into a semi-circular shape in the plane of the paper in FIG- URE 4. If fabricated in this shape, the movable walls would be in the form of semi-circular or circular annulii positioned parallel to each other and spaced from the ridges of the guide, which would also be of curved configuration. By making the nominal diameter of the aunular movable walls equal to the diameter of the diaphragm of an available speaker, the periphery of the cone of the speaker could be secured throughout most of its length to the movable walls (one speaker on each side). With this construction, all points of the movable plate will be driven rather than only the central section of the straight plate of FIGURE 5 (when one transducer is used), or at distributed points when a bank of smaller transducers is used.

As was mentioned earlier, the movable sidewalls may also be moved in and out by electrostatic transducers, one form of which is schematically illustrated in FIGURE 10. In this cross-sectional view, which corresponds generally to FIGURE 6, the movable sidewalls 16 and 18, formed of thin conductive material, are secured along their upper and lower edges to the upper and lower walls of the waveguide, provided with ridges 12 and 14, by flexible hinges 20, 22, 24 and 26 formed of flexible conducting material, such as aluminum foil. The hinges support the sidewalls closely adjacent the edges of the ridges to give a ratio of ridge width-to-guide with approximating one. Motion of sidewalls 16 and 18 parallel to themselves is produced by a pair of conductive plates 70 and 72, positioned closely adjacent the sidewalls and coextensive therewith, which are electrically charged oppositely to the movable walls 16 and 18 by a suitable high voltage, low current source, schematically illustrated as a variable battery 74. The movable sidewalls are attracted to the fixed plates 70 and 72 by the Coulomb force existing between the oppositely charged plates, the amount of deflection being determined by the difference in potential and the constraining forces offered by the hinges. By suitably modulating the high voltage source 74, the sidewalls may be moved out from a minimum initial position and back to the initial positron, by the restoring force due to the springiness of the hinges, to produce a variation in phase shift in the same manner as in the electromagnetically driven phase shifter described above. It will be understood that the internal construction of an electrostatically driven phase shifter (e.g., the transition section and ridge taper, etc.) would be the same as in the phase shifter using electromagnetic transducers.

From the foregoing it is seen that applicant has provid ed a phase shifter adaptable to electronic control, which produces a significant change in phase in a relatively short length of waveguide. This is possible through the utilization of ridged waveguide in which the ratio of ridge width-to-guide width approaches unity, and by varying the width ofthe gap between the ridge and the sidewalls by moving the sidewalls in and out in a controllable fashion. This construction, together with suitable transition sections in the region of the movable Walls, has a substantially uniform impedance throughout the range of phase shift capability of the device with the result that the phase shifter does not constitute an obectionable discontinuity in a signal line. A large change in phase shift is obtainable with very small wall displacements, readily achievable with available transducers.

While there have been illustrated and described what are considered to be preferred embodiments of applicants invention, various modifications will now be apparent to ones skilled in the art without departing from the true spirit thereof. For example, dimensions other than those suggested obviously can be used as dictated by the operating frequency and power handling requirements. In this connection, it is emphasized that the specific embodiment which has been described herein has a b /b ratio slightly greater than two, a condition for which w is not as sensitive to changes in the a /a ratio as it is at higher ratios of ti /b as shown in FIGURE 1. Thus, if the power handling requirements of the phase shifter will permit a smaller spacing between the ridges than that which gives a ratio of about two, the amount of phase shift per unit length can thereby be increased. It appears theoretically possible to increase the 12 /17 ratio to at least ten, which will give a substantially greater phase shift per unit length than is depicted in FIGURE 9. Also, means other than the illustrated hinges might be used to allow in and out movement of the sidewalls, other forms or configurations of transducers might be employed to impart the requisite displacement to the sidewalls, or single ridge waveguide may be used instead of the described double ridge guide. It is the intention, therefore, that the invention not be limited to what has been shown and described except as such limitations appear in the appended claims.

What is claimed is:

1. A phase shifter comprising, a section of rectangular waveguide having top, bottom and side walls, a conductive ridge coextensive with said section on at least one of said top and bottom walls, said ridge being tapered at both ends from a first width to a second width which approaches the wid.h dimension of said waveguide to provide narrow spaces between said side walls and said ridge throughout the length of said section between the tapered ends of said ridge, means resiliently mounting said side walls along their upper and lower edges to said top and bottom walls, respectively, and means arranged to move said side walls substantially parallel to themselves to controllably vary the width of said spaces.

2. Apparatus in accordance with claim 1 having confronting ridges on both said top and bottom walls and electrically actuable transducers coupled to said. side walls for varying the width of said spaces.

3. A phase shifter comprising, a section of rectangular double ridge waveguide having top, bottom and side walls, said ridges being of substantially equal, uniform width throughout a central portion and tapered at both ends from said uniform width to a narrower width, said. uniform width approaching the width dimension of said wave guide to provide narrow spaces between said side walls and said ridges throughout said central portion, means resiliently mounting said side walls along their upper and lower edges to said top and bottom walls, respectively, and at least one transducer coupled to each of said side walls operative when energized to vary the width of said spaces.

4. Apparatus in accordance with claim 3 wherein each of said transducers comprises an electromagnetic speaker including a movable cone secured to one of said side walls.

5. Apparatus in accordance with claim 4 including a plurality of transducers secured to each of said side walls and distributed along the length thereof.

6. Apparatus in accordance with claim 3 wherein each of said transducers includes a conductive plate supported closely parallel to a respective side wall of said waveguide, and means coupled to said plate and said side wall and operative when energized to oppositely electrically charge said plate and said side wall whereby said side wall is attracted toward said plate to increase the width of the space between said side wall and said ridges.

7. A variable phase shifter comprising, a section of rectangular double ridge waveguide having top, bottom and side walls, said ridges being uniformly spaced apart throughout the length of said section a distance such that the ratio of the spacing to the height dimension of said guide is at least two, and of substantially equal, uniform width throughout a central portion and uniformly tapered at both ends from said uniform width to a narrower width at the ends of said section, said uniform width being slightly less than the width dimension of said waveguide to provide narrow spaces of substantially equal and uniform width between said ridges and said side walls throughout the length of said central portion, hinges of flexible conductive material co-extensive with said section of waveguide securing said side walls along their upper and lower edges to said top and bottom walls, respectively, and at least one transducer coupled to each of said side walls operative when energized to move said side walls parallel to themselves to vary the width of said spaces.

8. Apparatus in accordance with claim 7 further including flexible hinges securing the end edges of said side walls to said waveguide.

'9. Apparatus in accordance with claim 7 wherein each of said transducers comprises an electromagnetic speaker including a movable cone secured to the exterior of one of said side walls, said speaker being operative when energized by a signal current to move said. side wall in and out relative to a rest position to thereby decrease and increase the width of the space between said side wall and said ridges.

10. Apparatus in accordance with claim 7 including a plurality of transducers secured to each of said side walls distributed. along the length thereof and each comprising an electromagnetic speaker including a movable cone secured to the exterior of said side wall.

11. Apparatus in accordance with claim 7 having a single transducer for each side wall, each comprising a conductive plate having an area comparable to that of said side wall, and means coupled to said plate and said side wall and operative when energized to oppositely electrically charge said plate and said side wall whereby said side wall is attracted toward said. plate to increase the width of the space between said side wall and said ridges in proportion to the amount of charge.

12. For the transmission of wave energy from a first waveguide section to a second waveguide section having movable side walls, a first rectangular waveguide section having rigid top, bottom and side walls and having an output end, a second rectangular waveguide section having rigid top and bottom walls and side walls adapted to be moved parallel to themselves, and having an input end, at least the top and bottom walls of said first section being conductively joined at its output end to the top and bottom walls at the input end of said second section, said second waveguide section having like confronting ridges centrally located on the top and. bottom walls thereof, said ridges being uniformly tapered from a first width at the junction of said first and second sections to a greater uniform width which approaches the width dimension of said second section to thereby provide narrow space be- .tween said movable side walls and the edges of said ridges.

13. Apparatus in accordance with claim 12 further including means for resiliently securing the ends of said movable side walls at the input end of said second. section to the side walls of said first section.

14. Apparatus in accordance with claim 13 wherein said means for resiliently securing said movable side walls is formed of thin conductive material.

15. A phase shifter comprising, a section of rectangular double ridge waveguide having top, bottom and side walls, means resiliently connecting said side walls along their upper and lower edges to said top and bottom walls, respectively, said side walls being parallel to and closely adjacent the sides of said ridges to provide spacings between said side walls and said ridges of a width such that the ratio of ridge width to guide width approaches unity, and means for moving said side walls substantially parallel to themselves to controllably vary the width of said spacings.

16. A phase shifter comprising, a section of rectangular ridge waveguide having top, bottom and side walls, means resiliently connecting said side walls along their upper and lower edges to said top and bottom walls, respectively, said side walls being parallel to and closely adjacent the sides of said ridge to provide spacings between said side walls and said ridge of a width such that the ratio of ridge width to guide width approaches unity, and means for moving said side walls substantially parallel to themselves to vary the width of said spacings.

17. A phase shifter comprising, a section of rectangular 2,567,748 9/1951 White 333-95 ridge waveguide having top, bottom and side walls, means 2,590,511 3/ 1952 Craig et a1. 33395 resiliently connecting said side walls to said top and bot- 2,602,893 7/ 1952 Ratliff 33395 tom walls, said sidewalls being parallel to and closely 2,602,895 7/1952 Hansen 33395 adjacent the sides of said ridge to provide spacings be- 5 2,659,817 11/1953 Cutler 333-95 tween said side walls and said ridge of a Width such that 3,118,118 1/1964 Watts 333-31 the ratio of ridge width to guide width approaches unity, 3 132 312 5 1964 Carey et 1 333 31 and means for moving said side Walls substantially parallel to themselves to vary the width of said spacings. OTHER REFERENCES 10 Proc. IRE, vol. 35, pp. 738-88, Ridge Wave-guides,

References Cited by the Examiner August 1947 UNITED STATES PATENTS 2,433,368 12/1947 Johnson et a1. 333 95 HERMAN KARL SAALBACH, Przmary Exammer.

2,461,005 2/1949 Southworth- 333-95 ELI LIEBERMAN, Examiner. 

1. A PHASE SHIFTER COMPRISING, A SECTION OF RECTANGULAR WAVEGUIDE HAVING TOP, BOTTOM AND SIDE WALLS, A CONDUCTIVE RIDGE COEXTENSIVE WITH SAID SECTION ON AT LEAST ONE OF SAID TOP AND BOTTOM WALLS, SAID RIDGE BEING TAPERED AT BOTH ENDS FROM A FIRST WIDTH TO A SECOND WIDTH WHICH APPROACHES THE WIDTH DIMENSION OF SAID WAVEGUIDE TO PROVIDE NARROW SPACES BETWEEN SAID SIDE WALLS AND SAID RIDGE THROUGHOUT THE LENGTH OF SAID SECTION BETWEEN THE TAPERED ENDS OF SAID RIDGE, MEANS RESILIENTLY MOUNTING SAID SIDE WALLS ALONG THEIR UPPER AND LOWER EDGES TO SAID TOP AND BOTTOM WALLS, RESPECTIVELY, AND MEANS EDGES TO SAID TOP AND BOTTOM WALLS SUBSTANTIALLY PARALLEL TO THEMSELVES TO CONTROLLABLY VARY THE WIDTH OF SAID SPACES. 